38 lines
863 B
TypeScript
38 lines
863 B
TypeScript
import { Controller } from '@nestjs/common';
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import assert from 'assert';
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@Controller()
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export class EANService {
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// https://en.wikipedia.org/wiki/International_Article_Number#Calculation_of_checksum_digit
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calcChecksum(id: string) {
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assert(id.length === 12);
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let sum = id
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.split('')
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.map((d) => parseInt(d, 10))
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.reduce((s, d, i) => s + d * (i % 2 === 0 ? 3 : 1), 10);
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while (sum >= 10) {
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sum -= 10;
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}
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return sum;
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}
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isValid(ean: string) {
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return this.calcChecksum(ean.slice(0, 12)) === parseInt(ean[12], 10);
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}
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toID(ean: string) {
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if (ean.length === 12) {
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// it already is an ID
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return ean;
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}
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if (!this.isValid(ean)) {
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throw new Error(`Invalid EAN: "${ean}"`);
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}
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}
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fromID(id: string) {
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assert(id.length === 12);
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return id + this.calcChecksum(id);
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}
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}
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